Many medicament delivery devices are arranged with a number of automatically triggered functions such as penetration, injection, withdrawal and/or protection of a medicament delivery member after delivery, just to mention a few.
Many of these functions require a number of components, making the device rather complex, as well as requiring handling aspects that may be difficult to perform for some users, even though the functions as such are automatic. There are also aspects regarding the interaction between different components requiring handling tolerance chains that may be quite complex when a number of components are to interact.
In many devices it is thus a preferred to keep the number of components as low as possible in order to reduce the complexity of the functions as well as reducing the tolerance chains. Also in view of handling and administration of medicament the number of components of the device should be kept as low as possible in order to provide a clear and concise operation. Regarding manufacturing aspects, it is also often desired to have as few components as possible and/or to provide several functions in one component.
In order to keep the number of components as low as possible, some devices use one single spring for both a penetration operation as well as a subsequent injection operation. A common solution is then to let the single spring act on a plunger rod, which in turn acts on a stopper inside a medicament container. The plunger rod then pushes the medicament container in the proximal direction in order to perform a penetration.
The movement in the proximal direction is possible because the medicament is incompressible and because the passage through the medicament delivery member is very small. However, some medicament will be expelled during penetration, which may be a clear drawback for some treatments where it is important that the medicament is delivered at a certain predetermined depth of penetration.
In all, there is room for improvements in the area of medicament delivery devices arranged with several functions.